Orange, Yellow Purple – Is there a difference? Which one is harder? What does the color mean? But I’m just looking for a slightly sportier feel. Is Urethane the same as Polyurethane? All of these questions, and more, will be answered.
What does it all mean?
I’ll save you the suspense – Urethane IS Polyurethane, just in a different form. And color means nothing in terms of performance. Some suppliers use a signature color to represent their company. Some companies don’t care what color is used. And some companies use colors to differentiate batches due to a slightly altered methodology of production or in other terms, a ‘date code’ identifier.
Yes, 95A is indeed harder than 80a and will give a sportier feel in the application of suspension and drivetrains. More on that later. But because 95A is harder than 80A, it is much more easily machineable (turning, facing, drilling, boring…etc). But why is it actually harder or softer? For all intents and purposes, Urethane is the same as Polyurethane. Urethane is the monomer (ethyl carbamate). Basically, polyurethane is a long chain of urethane molecules, and they are bonded front to back, front to back, and so on....
The answer at a high level is: Isocyanates*, Polyols, and Crosslinking. Flexibility is attributed to the polyol, which is a soft, elastic polymer and its reaction with the Isocyanates (averaging 2 or more groups per molecule).
The theory is that high amounts of crosslinking within short chains combined with lower molecular weight polyols give tough or rigid polymers. Conversely, long chains, low crosslinking, and a higher molecular weight polyol give a polymer that is very stretchy.
Polyurethane crosslinking allows the polymer to be a three-dimensional network. As a result, the overall molecular weight is very high and allows polyurethanes the property of not softening up when heated, aka ‘thermosetting polymers’.
Polyurethane was invented during the WWII era by the German Professor, Dr. Otto Bayer (1902-1982), known as the “father” of the poly industry. From there, polyurethanes can be found in adhesives, coatings, foams and finally flexible foams in the late 50’s. Today, you can see polyurethanes in virtually anything, including structural moldings for anything you see. Footwear, appliance, home, garage…etc. This is all great, but here we’re going to discuss how polyurethanes have shaped our automotive aftermarket culture for use specifically in swapped BMW’s.
Durometer (more commonly known as ‘Shore’) is nothing more than a measure of hardness. And within that, there are several different scales. Most common is the ASTM D2240 Type A for polyurethanes. Hence the “A” at the end of the number. (examples: 70A, 80A, 95A). Scale is from 0 to 100. The higher the number, the harder the polyurethane. A calibrated instrument is used to provide a very specific force to a poly of certain dimensions, creating an indentation in the material. The machine holds its indented force in the poly for 15 seconds, then is released. Immediately thereafter, the indentation is measured for depth. For shore “A”, a hardness range of 100-0 is proportional to the depth of (0.0” – 0.1”+). Aka, no indentation, the harder the material and therefore a durometer of 100 is assigned. Durometer is a dimensionless quantity. And because of that, there are many scales depending on the standard that’s used and the best scale is chosen based on the properties of the polyurethane. Here is a quick scale below of the durometer and the scale used for various materials. Again, most if not all automotive applications deal with shore, or scale “A”.
Now that you know about the history of polyurethane, how it works, and how it’s measured hardness works, how about common-day applications.
You don’t always need 95A all around or 80A all round on your e30. Sometimes it’s critical to have harder poly on some areas of your e30 while softer on others. Factory e30 rubber mounts for most applications, including oil filled motor mounts are in the 60A-65A range. That’s pretty soft, but to give you comparison compared to stock, see below.
60-65A - Stock e30
70A – 25% stiffer
80A – 30-35% stiffer
95A – 75-80% stiffer
While the 60A-65A bushings do result in a lot of engine movement, especially during hard acceleration, the benefit is a comfortable driving experience and less noise transmission through your e30.
For that perfect balance, I recommend Garagistic’s 80a e30 mounts.
Just a quick list of the benefits of Polyurethane bushings over stock e30 rubber.
- It allows your e30s suspension to react quicker to changes in road conditions, quicker steering, more responsive and receptive to your inputs as the driver. As a result, the power lost in the soft bushings is actually going right to your wheels!!
- Polyurethane is easy to install, no presses or special tools needed!
- Polyurethane outlasts rubber bushings. In most applications, it will last the life of your daily road driven e30!
- You can get custom offset fitment for race applications to help with wheel alignment, ride height…etc.
Want to go delrin on your e30? or even crazier and get solid bushings? Not a problem, only it is. If you daily drive your E30 and want to go delrin or solid, the ancillary setback is that the E30 chassis itself is not particularly designed for this type of vibration from the drivetrain and the roads. And because of that, things happen. Connectors dislodge, pins and electrical connections come loose, screws slowly back out and some bolts loosen up. For a car manufacturer to design to those strict requirements of solid mounted bushings, the car would look like a tank. You can use delrin or even a solid mounted configuration, but just beware of the long term consequences on your e30 due to daily driving around town.
What else does Garagistic offer?
Thanks for reading and stay tuned for more posts. At least 2 new posts per week, with one of them guaranteed to be dedicated to the ongoing E30-LS1 project!!
* Recent efforts are attempting to minimize the use of isocyanates to synthesize polyurethanes, because the isocyanates raise severe toxicity issues. Non-isocyanate based polyurethanes (NIPUs) are in the works as a new class of polyurethane to alleviate environmental concerns.
Thanks to wikedia, McMaster for the information